How does RealVNC know when to make a screen capture

Corné Beerse cbeerse "at"
Tue Jan 6 16:32:01 2004

Castelier Serge (RBFM/ASQ1) * wrote:
> Hello
> I downloaded the source code of VNC and had a look at it.
> Apparently VNC makes screen captures for a Win32 PC by using API's such as
> GetDIBits(). But it's not clear to me how the server part of the application
> knows that something has changed on the screen of the PC. Furthermore ,I don't

It does not know that. That's why you can configure several polling options in 
the vncserver. It just peeks at some regular interval or when it expects 
differences (like mouse or keyboard actions).

> know if VNC makes a screen capture of the entire screen or just of the part
> that has been changed.

That's also one of the polling options.

> I saw in the source code that regions are beeing used with API's such as
> GetRegionData() and I gather VNC is using regions to determine which part of
> the screen has to be refreshed, but I'm not  familiar with regions and I
> didn't manage to understand how it works.

In the end, I expect/experienced it does just some matrix over the polled area 
and sends the updated rectangles. I don't know for sure.

> Can anyone help me ?
> Thank you in advance
> Serge Castelier
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